A great deal of importance has been attached to resolving problems of quality and reliability in the manufacture of various materials, for example steel, and particularly the connection or seams between them, formed by welding, soldering or any other method. There are many well-known methods and devices available for controlling the quality of connections between metals. The discovery of faults in structures and machines is highly important; however, existing probes/detectors are frequently inaccurate, particularly when testing "Austenite" type steel, which is comprised of relatively large granules. The sensitivity of these devices is particularly low with regard to faults in "Austenite" type steel, and the need to improve these tests has become more acute in view of the accidents which have occurred in nuclear reactors.
One of these devices is described in U.S.S.R. Inventors Certificate No. 962806. This flaw detector is based on two ultrasonic vibration converters located in a single box, wherein one converter includes a panel which radiates focused energy and the other converter includes an identical panel which receives the ultrasonic radiation reflected from the product being tested. The converter panels used for the radiation and reception of focused ultrasonic radiation are made of a piezoelectric material. The echo method enables external and hidden flaws to be revealed in complete and semi-complete products of various sizes and shapes, flaws which cannot be discovered by other means.
During the test, the device moves over the surface of the material being tested, so that the focused energy is penetrated into the mostly metal product. This device radiates focused energy into the product in the form of a series of ultrasonic impulses (short pulses separated by a relatively long interval). Reflected energy is returned to the device from the metal granules, for example, of the Austenite type, which are relatively large. As stated above, the sensitivity of the known detectors for Austenite type metal is very low, while the new device is far more sensitive and capable of discerning flaws which cannot be identified by means of current devices. If the process is completed within a reasonable period of time and in a regular fashion, then the metals and the seams between them may be considered normal. However, if any change takes place in the time required by the operation or in the form of the ultrasonic ray's reflection, this is an indication of some flaw. If a flaw falls in the way of the ultrasonic impulse--then the recorded reflected impulse carries information regarding the flaw from which the focused energy was reflected, and this information is analyzed within the device or by means of peripherals connected to it. Thus, the time elapsing from the transmission of an impulse to the reception of the reflected impulse, indicates the distance between the device and the flaw; the size of the reflected impulse indicates the size of the flaw.
In the instruments currently in use, the converter panels are made of a single piece of a piezoelectric material, either straight or curved, and their parameters is the fact that at various points along the length and breadth of the panel they have different magnitude. Thus, different points of these panels have non-uniform electric and mechanical parameters, and the magnitude of certain parameters at one point can be greater by hundreds of percents than its value at another point on the same panel. This leads to tremendous difficulties in the manufacture of such devices, with the consequence that a high percentage of these devices are flawed immediately following their assembly at the plant (usually, more than 50%). As noted, one drawback of the probes/detectors in current use is their complex production, particularly given that the piezoelectric panels are shaped as part of a cylindrical surface. Because of the relative large required size of the piezoelectric panel, its mechanical and electric parameters at various points are unequal and this creates difficulties in the design of the probes characteristics. The inventors are not aware of any device capable of resolving these problems, with the exception of the device detailed below.